1. Field of the Invention
The present invention relates to an image forming apparatus provided with a process unit which integrally supports a photoconductive drum and process devices disposed opposite to a surface of the photoconductive drum, which process unit is attachable to and detachable from a predetermined position of the apparatus, wherein the photoconductive drum of the process unit attached to the apparatus is rotated by driving force supplied from a driving mechanism thereto.
2. Description of the Related Art
In an image forming apparatus which performs an image forming process by electrophotography of forming an electrostatic latent image on the surface of a photoconductor by the action of photoconduction and transferring a developer image obtained by making the electrostatic latent image manifest, onto a sheet of paper, not only a developer is consumed, but also a process device such as a photoconductor or a charger is exhausted, so that it is required to replace a process device which has been used for a predetermined period of time. As such an image forming apparatus which performs the image forming process by electrophotography, there is an image forming apparatus in which process devices including a photoconductor which are used in the image forming process are combined into one unit and detachably integrated with the apparatus body, whereby a replacement operation of a process device is facilitated.
Among the process devices included in the unit attachable to and detachable from the apparatus body as described above, the photoconductor is to rotate at a fixed speed during the image forming process, so that it is required to prepare a component for transmitting driving force from a driving mechanism in the apparatus body to the photoconductor in the unit attached to the apparatus body.
For this reason, a conventional image forming apparatus is designed so that a coupling member which is placed on a photoconductor is engaged with a coupling member which is placed on a frame of the apparatus body when the unit is attached to the apparatus body, and so that a driving force from a driving mechanism of the apparatus body is transmitted to the photoconductor through the engagement of both the coupling members.
For example, Japanese Unexamined Patent Publication JP-A 58-152262 (1983) discloses such a configuration that the unit is provided with a driving coupler (a coupling member on the unit side) to which a driving transmission mechanism on the apparatus side (a coupling member on the apparatus side) is coupled, to attach the unit to the apparatus body at a predetermined position by using convex parts which are formed around the driving coupler. These convex parts are a connector for a charger, a connector for a developing device, and a detent pin, which are respectively engaged with a connector of an electric power source for a charger, a connector of an electric power source for a developing device, and a slot, of the apparatus body.
Further, Japanese Unexamined Patent Publication JP-A 52-149125 (1977) and Japanese Unexamined Patent Publication JP-A 55-52080 (1980) disclose a configuration of fitting a photoconductive drum to a drum shaft (a rotating drive shaft), and thereafter securing the photoconductive drum tightly to the drum shaft by a nut.
However, in such a configuration of attaching the unit to the apparatus body as adopted in the conventional image forming apparatus disclosed by JP-A 58-152262 and so on, the photoconductive drum and other process devices such as the charger or the developing device of the unit are respectively positioned in the apparatus body via individual coupling members, so that there is a problem such as the image quality is degraded due to a difference and skewness in an image forming position on the surface of the photoconductive drum.
This is because a fitting position of the photoconductive drum to the apparatus body is determined without reference to fitting positions of the other process devices one another to the apparatus body, and the fitting position of the photoconductive drum and the fitting positions of the other process devices make differences individually relative to the apparatus body, with the result that a difference is made in a positional correlation between the photoconductive drum and each of the other process devices.
In an image forming apparatus which adopts a digital exposure system of performing exposure by image light for each one line in the direction of main scanning, positions where the other process devices perform processes to the surface of the photoconductive drum affect on an image forming status significantly, and the image quality is easily degraded due to positional differences between the photoconductive drum and the other process devices, so that the problem mentioned above is especially critical in the image forming apparatus adopting the digital exposure system.